1. Field of the Invention
The invention relates to an electrostatic discharge (ESD) protection circuit, and in particular relates to an electrostatic discharge (ESD) protection circuit with low leakage, high trigger speed and parasitic silicon controlled rectifier (SCR).
2. Description of the Related Art
FIG. 1 shows a conventional electrostatic discharge protection circuit 100. The conventional protection circuit 100 has an electrostatic discharge detecting circuit 110, and the electrostatic discharge detecting circuit 110 has a trigger node 106. The trigger node 106 of the electrostatic discharge detecting circuit 110 is coupled to a silicon controlled rectifier 112. When an event of the electrostatic discharge occurs, the trigger node 106 produces a trigger current to trigger the silicon controlled rectifier 112. After the silicon controlled rectifier 112 is triggered by the trigger current, the silicon controlled rectifier 112 provides a discharge path to discharge the electrostatic discharge current from the rail VDD to the rail VSS.
With the progress in process techniques, new process techniques are able to reduce the size of metal-oxide-semiconductor field effect transistor (MOSFET) into a nanometer order. Thus, the leakage current of the gate oxide of metal-oxide-semiconductor field effect transistor (MOSFET) is increased, because the thickness of the gate oxide is reduced. The on-chip electrostatic discharge protection circuit, particularly the MOS capacitor, usually adopts a large size metal-oxide-semiconductor field effect transistor (MOSFET) when designing the circuit. Therefore, the electrostatic discharge protection circuit suffers from leakage current and inefficient system power usage in normal operating mode. To solve the leakage current of MOSFETs, most of the conventional electrostatic discharge protection circuits use a thick oxide device with high mask costs and low protection ability against electrostatic discharge, such that the electrostatic protection circuits require more space to improve the protection ability. Therefore, a low leakage electrostatic protection circuit is in need.